1. Field of the Invention
The present invention relates to a tension module, and more particularly to a built-in module for an inverter and having tension control with integrated tension and velocity closed loops.
2. Description of Prior Art
For machine equipment of papermaking, metal-manufacturing, textile, plastic-manufacturing, or cable industries, a tension-balance control is an essential and important requirement to ensure consistent qualities of manufactured products.
PID (Proportional-Integral-Derivative) controllers are focused much attention and are most commonly used in industrial control because the PID controllers are simple and easy to implement. More particularly, the PID controllers can be employed to eliminate steady-state errors and to obtain relative stability and damping characteristics of controlled systems.
Nowadays, a line speed control is the major control scheme for a tension control system which is built in an inverter. In this scheme, however, the line speed (not the tension force) is the major controlled variable. Thus, an unbalanced tension control tends to happen due to inconsistent line speeds when machine equipment is instantaneously started or stopped and even is operated under a tremendous speed-varying condition.
Reference is made to FIG. 1 which is a schematic view of providing a tension control for a winding mechanism by driving a motor through a prior art inverter. The scheme of the tension control for the winding mechanism mainly includes two inverters (namely, a first inverter 14a and a second inverter 24a) and two motors (namely, a first motor 12a and a second motor 22a). The winding mechanism is referred to as a controlled mechanical system 100a. The controlled mechanical system 100a mainly includes a first rotating shaft 10a, a second rotating shaft 20a, a winding object 30a, and a sensing unit 40a. The first rotating shaft 10a and the second rotating shaft 20a are used to rotate the winding object 30a in the winding process. The first inverter 14a is electrically connected to the first motor 12a, and the first motor 12a is mechanically connected to the first rotating shaft 10a. The first inverter 14a is provided to drive the first motor 12a to rotate the first rotating shaft 10a. Similarly, the second inverter 24a is electrically connected to the second motor 22a, and the second motor 22a is mechanically connected to the second rotating shaft 20a. The second inverter 24a is provided to drive the second motor 22a to rotate the second rotating shaft 20a. In addition, the first motor 12a and the second motor 22a further install a first encoder 16a and a second encoder 26a onto a shaft to measure the angular velocity thereof, respectively, in a closed-loop velocity control.
The sensing unit 40a is installed between the first rotating shaft 10a and the second rotating shaft 20a. The sensing unit 40a can be a tension sensor or a line speed sensor to sense the magnitude of the tension force and the velocity of the winding object 30a between the first rotating shaft 10a and the second rotating shaft 20a, respectively. Furthermore, the sensed magnitude of the tension force and the sensed velocity are used for a closed-loop tension control and a velocity control.
However, the use of either the tension sensor or the line speed sensor results in higher equipment costs and different feedback sources. Thus, it is not convenient for users to adjust and control the conventional inverters with tension control functions because different control modes and parameters have to be properly set.
Accordingly, it is desirable to provide a built-in module for an inverter and having tension control with integrated tension and velocity closed loops for an easy-use, high-acceptable, and wide-applicable tension-balanced control without any sensor.